1. Field of the Invention
This invention relates to methods of and apparatus for connecting optical fibers. In particular, it relates to elastic one-piece splicers for optical fibers, optical fiber connectors utilizing fiber-to-connector splice means, and to related methods. Accordingly, it is a general object of this invention to provide new and improved methods and apparatus of such character.
2. Description of the Prior Art
(a) Dual eccentric plugs have been used for connecting optical fibers. The fibers are epoxied into two cylindrical plugs, slightly off axis, and polished flat. The plugs are mounted with their axes parallel, but not co-linear. The plugs are rotated, with respect to each other, until the axes are co-linear, when maximum light throughput is achieved. Disadvantageously, such plugs required elaborate attachment of fiber and end preparation. Also, access was required to other ends of the fibers so that optical transmission could be monitored and optimized.
(b) Micromanipulator-assisted epoxy or fused splice. The fibers are manipulated in air, preferably with five degrees of freedom, for optimal alignment. Then, a drop of epoxy is applied to the fibers and cured. Alternatively, an arc melts and fuses the fibers. The manipulators can then be removed. Disadvantageously, micromanipulators are expensive. Also, to optimize alignment, either optical transmission should be monitored as above, or the ends should be watched with a microscope from two different angles.
(c) Alignment V-groove. Two fibers are brought together while being forced to the bottom of a groove, then either clamped or epoxied in place.
Disadvantageously, precision parts and insertion techniques are required. It was common to end with fiber ends separated too far or overlapping.
(d) Snug-fitting metal or glass capillary tube. Superficially similar to present invention, but requiring precision tolerances for alignment in a rigid tube rather than symmetric elastic forces. Disadvantageously, rigid capillary tube splicers require precision tolerance fits to a particular fiber size. When a fiber is too large, it does not fit in; when a fiber is too small, it does not hold on axis. Unfortunately, tolerances for axial alignment are generally somewhat tighter than manufacturing tolerances on fiber diameters; a tube that fits snugly on one fiber does not necessarily fit well enough on the other fiber to be spliced.
(e) Most commerical optical fiber connectors have the following basic principle of their connector design philosphy in common: the ends of the fibers to be connected are themselves brought together and separated with each connect/disconnect cycle, with the connectors serving only to align them precisely each time and hold them together securely. Various types of interface configurations have been used when the ends were brought together; intimate glass-to-glass contact, precise tolerance air gap (less than one mil apart), index-matching fluids, lenses, and buffer membranes, for example.
(f) Many successful connectors of the prior art, in terms of low insertion loss and simplicity of use, have been those that are installed onto the ends of a fiber at a factory, and cannot be installed by a user in the field. An example of this is a connector available from one manufacturer, in which a fiber end is epoxied into a machined plug, the fiber and plug are polished flat to a high optical quality, and the plug is then installed into a connector body with precise alignment of the fiber axis along the axis of the connector--all at the factory. The user makes the connection by screwing each connector end into a central axis-aligning section until the plugs meet. The precise factory machining and alignment account for the connector's low insertion loss and quick connecting means, but also results in extreme inflexibility when installing, changing, testing, or repairing an optical fiber system. Disadvantageously, such factory-installed connectors have been only obtainable attached to specific lengths of fiber, which cannot be altered or repaired in the field.
(g) A second manufacturer offers a commercially available, relatively easily field-installable connector. A fiber is cleaved and clamped into a connector end. This is then inserted into a central section where the fiber end is guided into a precisely molded dimple in a plastic disc. The dimple is filled with an optical gel which forms a gel lens whose two optical surfaces are the flat fiber end and the molded plastic surface. The two fibers, one on each side of the plastic disc, form two gel lenses which serve to image the light from one fiber into the other. Disadvantageously, such connectors have short sections of easily damaged bare fibers exposed when disconnected. The optical gel can trap dust particles and air bubbles, especially after a number of connect/disconnect cycles, which can cause significant light losses. Slight fiber cleaving irregularities alter the shape, and thus the performance, of the gel lens.
(h) A third manufacturer offers a precision connector, similar to that discussed at (f) above, that can be installed in the field. Disadvantageously, the use of such connectors requires that field technicians learn the fine art of optical polishing, and perform it in a field environment, rather than a controlled optics shop with proper facilities. The reliability of such connections is questionable.